1. Field of the Invention
The present invention relates to complex elements for an antenna of a radio frequency (RF) repeater and a dipole array circular polarization antenna using the same, and more particularly, to complex elements for an antenna that is used in a radio frequency (RF) repeater system and that generates circular polarization, and a dipole array circular polarization antenna using the same.
2. Description of the Related Art
In a wireless network of a mobile communication system, due to nature and artificial obstacles such as mountains or buildings, tunnels, insides of buildings, etc., the intensity of propagation is reduced, and a shadow region in which reception of a radio frequency (RF) from a mobile terminal is not possible, is formed. A RF repeater re-amplifies base station signals to cover the shadow region that exists in a service area of a base station so that a good service can be provided to a user any time and any where. In the RF repeater, the shadow region can be removed by the simplest way.
In the RF repeater, a donor antenna for transmitting and receiving RF signals to and from the base station, and a service antenna for transmitting and receiving RF signals to and from a terminal are connected to each other. Downlink signals from the base station to the terminal are received by the donor antenna, are amplified by the RF repeater and then are transmitted to the terminal through the service antenna. Uplink signals from the terminal to the base station are received by the service antenna, are amplified by the RF repeater and then are transmitted to the base station through the donor antenna.
Generally, the donor antenna and the service antenna have directivity. Thus, it is idealistic that propagation is radiated only in a forward direction of an antenna. However, in the case of an actual antenna, propagation is not radiated only in the forward direction of the antenna but propagation is partially radiated even in a backward direction of the antenna. In this case, the ratio of intensity of propagation radiated in the forward direction to intensity of propagation radiated in the backward direction is a forward/backward ratio. As the forward/backward ratio increases, i.e., as the intensity of propagation radiated in the forward direction is large, an idealistic antenna is constituted.
In the case of the RF repeater, the donor antenna and the service antenna are in opposite directions. Since transmission and reception frequencies of each of the donor antenna and the service antenna are same, the frequency of a signal transmitted from the service antenna (or the donor antenna) and the frequency of a signal received from the donor antenna (or the service antenna) are same. Thus, in the case of the conventional RF repeater, a signal transmitted from an antenna is fed back to another antenna and is input. The RF repeater is oscillated and a normal operation cannot be performed. To prevent this problem, isolation (a degree at which a plurality of adjacent antennas are not interfered with each another) between two antennas needs to be improved by increasing the forward/backward ratio of the donor antenna and the service antenna.
FIG. 1 illustrates the structure of a conventional RF repeater.
Referring to FIG. 1, the conventional RF repeater comprises a donor antenna 110, a service antenna 120, and a repeater unit 130.
The donor antenna 110 receives an RF signal from a base station 140 or transmits the RF signal that is received from a wireless terminal 150 through the service antenna 120, to the base station 140. The service antenna 120 receives the RF signal from the wireless terminal 150 or transmits the RF signal that is received from the base station 140 through the donor antenna 110, to the wireless terminal 150. The repeater unit 130 filters and amplifies the RF signal between the donor antenna 110 and the service antenna 120.
In the RF repeater having the above structure, when separation between the donor antenna 110 and the service antenna 120 is not sufficiently gained, a signal that is re-transmitted through the service antenna 120 after the RF signal is amplified, is fed back to the donor antenna 110 so that the amplifier can be oscillated. Thus, a method of determining an amplification gain by which the separation between the donor antenna 110 and the service antenna 120 is gained to the maximum (generally, 60-70 dB) and a power amplifier is not oscillated, is used. In this case, since oscillation of the repeater is fatal to a network and a system, a gain of the amplifier is set to be 15-20 dB that is smaller than separation that is generally gained. Thus, the gain of the amplifier is about 40-55 dB, which limits a basic function of the repeater, i.e., a function of expanding a sufficient coverage or supplementing the shadow region and acts the greatest disadvantage of the RF repeater.
In addition, in the conventional RF repeater, since the donor antenna 110 and the service antenna 120 are disposed on same plane, directions of a main lobe and side lobes of each of the donor antenna 110 and the service antenna 120 are formed to the same height as an adjacent antenna in a horizontal direction. In this case, the main lobe and the side lobes that are directly reflected by ambient buildings or objects are vertically radiated in opposite direction to radiation direction, and interference occurs.
In order to prevent the interference due to the main lobe and the side lobes in the conventional RF repeater, an antenna for an RF repeater by using X-shaped dipole dual polarization radiation elements has been suggested. FIG. 2 illustrates a conventional plane-arranged circular polarization antenna for an RF repeater by using dipole dual polarization radiation elements.
Referring to FIG. 2, the conventional plane-arranged circular polarization antenna for the RF repeater by using the dipole dual polarization radiation elements comprises a plurality of radiation elements 210, a reflective patch element 220, an auxiliary reflective plate 230, and a feeding portion (not shown).
The plurality of radiation elements 210 are disposed on the reflective patch element 220 in a 4×4 arrangement and radiate incident propagation that is input through the feeding portion, in a form of right circular polarization or left circular polarization. Each of first through fourth radiation elements 310, 312, 314, and 316 is a -shaped conductor and constitutes the X-shaped radiation elements 210 by using first and second feeding members 320 and 330. In this case, the first feeding member 320 connects the first and third radiation elements 310 and 314, and the second feeding member 330 connects the second and fourth radiation members 312 and 316. In addition, electronic waves that are input to the first feeding member 320 and the second feeding member 330 are fed with a phase difference of 90°.
FIG. 3A illustrates the detailed structure of the radiation elements 210, and FIG. 3B illustrates the radiation shape of electronic waves radiated by the radiation elements 210.
Referring to FIGS. 3A and 3B, the radiation elements 210 comprise a plurality of radiation members 310, 312, 314, and 316, and a plurality of feeding members 320 and 330. In the radiation elements 210 having the above structure, when incident propagation having a phase difference of 90° is fed to each of the radiation members 310, 312, 314, and 316 through the feeding members 320 and 330, circular polarization that rotates once is radiated, as illustrated in FIG. 3B. FIG. 3C illustrates a horizontal radiation pattern at 2.17 GHz of the -shaped radiation elements 210. Referring to FIG. 3C, side lobes and rear lobes exist in the circular polarization that is generated by the corresponding radiation elements 210, and a forward/backward ratio of the circular polarization is equal to or less than 24 dB.
The reflective patch element 220 is in the form of a box having an opened upper portion. The radiation elements 210 are accommodated in the reflective patch element 220. In this case, due to the bottom surface and sidewalls of the reflective patch element 220, radiation propagation that is propagated in a backward direction is intercepted. In addition, the auxiliary reflective plate 230 is separated from the outside of the sidewalls of the reflective patch element 220 and additionally intercepts radiation propagation that is propagated in the backward direction. A feeding portion 240 feeds electronic waves so that a phase difference of 90° occurs sequentially in the radiation elements 210 each having a 2×2 arrangement that constitutes a 4×4 arrangement. Thus, radiation propagation is radiated by the elements 220 each having a 2×2 arrangement with a phase difference of 0°, 90°, 180°, and 270° in a sequence.
FIGS. 4A and 4B illustrate horizontal and vertical radiation patterns of the conventional plane-arranged circular polarization antenna for the repeater by using the dipole dual polarization radiation elements illustrated in FIG. 2. Referring to FIGS. 4A and 4B, the conventional plane-arranged circular polarization antenna for the RF repeater by using the dipole dual polarization radiation elements shows a side lobe level that is equal to or less than −25 dB in a horizontal radiation characteristic and shows a side lobe level that is equal to or less than −20 dB in a vertical radiation characteristic.
However, the conventional plane-arranged circular polarization antenna for the RF repeater by using the dipole dual polarization radiation elements described with reference to FIGS. 2 through 4B shows a good characteristic in the side lobe level. However, since a beam width is about 30°, a service area is reduced. In addition, in a feeding method, a plurality of phase delay elements need to be installed so as to feed electronic waves to each of the radiation elements so that a phase difference of 90° occurs, and an additional element for impedance matching is needed. As such, the size of the antenna increases and manufacturing costs thereof increase.